1. Field of the Invention
The invention relates to an absorbent batt structure formed from a loose assemblage of fibers that has enhanced fluid transport and fluid distribution characteristics. More specifically, the invention relates to an absorbent batt formed from a loose assemblage of fibers that has a discrete pattern of bonded compressed portions formed on at least one surface of the batt.
2. Description of the Prior Art
Disposable absorbent articles, such as diapers, have been provided with absorbent batt structures to receive and retain body fluids. Such absorbent structures are normally made from an assemblage of fibers, such as comminuted wood pulp known as "fluff". In recent years such structures have been provided with superabsorbent materials to enhance the fluid holding capacity of the batts. In order for the articles to function in a suitable manner, the absorbent structures should be capable of transporting the body fluids from the point of discharge to remote areas of the structure; thus distributing the fluids throughout the structure and minimizing saturation at the point of discharge.
It is known to use absorbent structures in such articles that are compressed to a relatively high degree throughout the structure. The compression of such structures may be maintained by hydrogen bonds or adhesive bonds between adjacent fibers. Although such structures may transport the fluid throughout the structure, these structures are not completely satisfactory since the fluid transport capability is accompanied with a loss of total absorptive capacity. These structures are also relatively stiff and do not conform to the shape of an infant when used in a disposable diaper as readily as an uncompressed structure. However, absorbent structures that are relatively uncompressed throughout the structure are not capable of adequately distributing fluids in the structure. Thus, there is a trade off between distribution or wicking capacity and absorptive capacity and flexibility of these structures.
In an attempt to solve these problems, various solutions have been proposed that provide absorbent structures that are compressed to a reduced thickness in certain portions thereof to provide relatively dense and less dense portions of the structure. In theory, the compressed portions of the structures serve to distribute fluids to spaced portions of the structure, while the uncompressed portions of the structures serve to retain fluids. Examples of various embodiments of such absorbent structures are disclosed in issued U.S. patents as briefly discussed immediately hereinbelow.
U.S. Pat. Nos. 2,905,568; 2,952,260; and 3,017,304 to Burgeni disclose cellulosic fibrous batts with a paper-like densified layer or portions formed on at least one surface thereof. The densified layer or portions are formed by applying moisture and pressure at the surface of the batt. The densified portions comprise a relatively large portion of the surface of the batt.
U.S. Pat. No. 3,060,936 Burgeni discloses an absorbent product having a core of comminute wood pulp fibers attached to a cover and a backing sheet by moistening a surface of the core and subjecting the cover sheet, backing sheet and the core to compression to bond the components together. A patterned or intermittent compression is applied to the components to form a series of spaced-apart compressed portions separated by relatively uncompressed portions.
U.S. Pat. No. 3,993,820 to Repke discloses an absorbent product comprising a cellulosic fibrous batt having a densified, paper-like layer which, in selected portions, is thickened with additional densified cellulosic fibrous materials. The thickened or more densified portions may be intermittent or discontinuous lines formed in the batt. The area of each thickened or more densified intermittent portion appears to be materially greater than the area of the less densified portions of the batt.
U.S. Pat. No. 3,766,922 to Krusko discloses a disposable diaper product comprising a profiled, embossed fluff batt of cellulosic fibers. The embossed pattern defines compressed, densified valleys or circular islands and uncompressed ridges. The ratio of the area of compressed islands in the middle region of the product is approximately 6% of the middle region. The compressed islands are approximately one-fourth inch in diameter and are spaced apart on one and one-half inch centers in rows spaced by three-eights inch. The patent indicates that, by reducing the area of the compressed islands in the middle region, the fluid storing capacity is enhanced without adversely affecting the fluid wicking characteristics of the middle region.
U.S. Pat. No. 3,886,941 to Duane et al. discloses a diaper insert product comprising an absorbent pad disposed between a liquid impermeable hydrophobic top sheet and bottom sheet. The top and bottom sheets have a plurality of valvular opening (slits) formed therein. A plurality of spaced-apart dimples are formed in the top and bottom sheets which form compressed portions therebelow in the absorbent pad. The compressed portions cooperate with the valvular openings to close the openings as the compressed portions expand upon saturation. The total area of the dimples is disclosed as being between 4% to 12% of the area of the absorbent pad. The dimple size is disclosed as being in the range of about 0.025 to about 0.250 inch in diameter. The regions between the dimples appear to be uncompressed.
U.S. Pat. No. 4,027,672 to Karami discloses an absorbent pad having densified portions and undensified portions. The densified portions have a thickness at least as large as the thickness of the undensified portions.
U.S. Pat. No. 4,443,512 to Delvaux discloses an absorbent article comprising an absorbent pad that is embossed on either side or both sides so as to form relatively highly compressed portions while the other portions thereof are substantially not compressed. The discrete compressed portions are alleged to enhance liquid dispersion characteristics while reducing wetback. The size of the densified portions is in the range of 0.01 cm.sup.2 to 2.0 cm.sup.2. The distance between the densified portions is in the range of 0.1 cm to 3.0 cm. The density of the uncompressed pad is in the range of 0.06 gm/cm.sup.3 to 0.12 gm/cm.sup.3 and the density in the densified portions is in the range of 0.10 gm/cm.sup.3 to 0.40 gm/cm.sup.3. The densified portions occupy between 10% to 80% of the surface of the article.
U.S. Pat. No. 3,692,622 to Dunning discloses a paper product, useful in sanitary wipes and toweling applications, comprising an absorbent web structure of wood pulp fibers having a basis weight of 5 to 50 lbs./2880 sq. ft. The structure is provided with hydrogen bonded areas that are produced by application of moisture and pressure. The total bonded areas for the web structure is in the range of 5 percent to 40 percent and preferably in the range of 8 percent to 20 percent.